1. Field of the Invention
The present invention relates to an attenuation reduction structure for circuit board, and in particular to an attenuation reduction structure for high-frequency signal connection pads of a circuit board with an insertion component.
2. The Related Arts
In various electronic devices that are used contemporarily, due to the amount of data transmitting through signal lines getting increasingly large, the number of signal lines involved is also getting larger and the frequency of the transmitted signal is higher. Differential mode signal transmission techniques have been widely used to suppress electromagnetic interference (IMF). For example, USB (Universal Serial Bus), LVDS (Low Voltage Differential signaling), and EPD (Embedded Display Port) have all widely adopted such techniques of signal transmission in order to suppress IMF.
Although the differential mode signal transmission can greatly overcome problems occurring in the transmission of signals, poor designs may still result in issues concerning signal reflection, dissipation of electromagnetic waves, missing or failure of transmission and reception of signals, and waveform distortion of signals. These problems of signal transmission are even worse for flexible circuit boards having a reduced substrate thickness. The causes of such problems include: poor matching of characteristic impedance in the longitudinal extension direction of differential mode signal lines, poor control of excessive parasitic capacitive effect between the differential mode signal lines and a grounding layer, poor control of excessive parasitic capacitive effect between a high-frequency connection pad zone and a grounding layer, and characteristic impedances of differential mode signal lines and a high-frequency connection pad zone being not matched.
Heretofore, various techniques have been proposed to overcome the impedance matching problems of differential mode signal lines of a flexible circuit board. However, at the site of connection between differential mode signal lines and a high-frequency connection pad zone formed on a flexible circuit board and the neighboring area thereof, the line widths of the differential mode signal lines (which are extremely small) and signal conduction pins of a connector and size specification of components (which are of a relatively large size compared to the line widths of the signal lines) impose limitations to the solution of such problems. Thus, it is an issue for those involved in this art to overcome the deficiency of the known techniques.